A variety of portable life support devices has previously been developed for use in hazardous work areas such as deep shaft mines. These devices are known as self-contained self-rescuer (SCSR) units. They typically provide an oxygen supply for breathing for up to one hour to give a miner time to escape conditions where there are toxic fumes present in the mine.
In previously available SCSR units, the need for extended service was balanced with portability. The desired one hour of breathable air has been provided with compressed oxygen or air supplies or oxygen generation systems, generally in combination with a carbon dioxide absorbent. Such systems often have the components included in cannisters or tanks. High pressure tanks, in turn, require heavy pressure regulators to step down the high pressure of the compressed gas to the low pressure required for breathing bag inflation. In those systems which rely on chemical generation of oxygen, the reactions involved are generally exothermic, so that the heat generated must be dissipated in a heat exchanger before the air can be breathed, further adding to both bulk and weight.
These and other factors have resulted in systems which, while providing an hour of breathable air, are too heavy and bulky to be worn continuously by miners while they work, or even to be carried easily and placed immediately adjacent the work area. Accordingly, curently available SCSR units are generally stored in central storage locations around a mine, which makes them less accessible to miners for rapid deployment in an emergency.
In addition to increasing portability, it would be desireable to increase the useful supply of breathable air in such apparatus, since one hour is sometimes marginal to ensure safe evacuation by miners in the event of an emergency.